1. Field of the Invention
During the last decade, research on vitamin D has lead to the recognition that vitamin D is the precursor of a new steroid hormone, namely 1,25-dihydroxyvitamin D. This is the substance which controls the translocation of calcium through the cells of instestine, bone and kidney. Efforts to measure this hormone have encountered difficulties, because of its instability, low concentration (normal levels 0-40 pg/ml) and, more significantly, because of the necessity for its separation from other metabolites of vitamin D of similar structure which circulate at much higher levels (25(OH)D.sub.3 -normal levels of 20-40 ng/ml; 24,25(OH).sub.2 D.sub.3 -normal levels 2-5ng/ml).
While assays have been developed, they have proven laborious, expensive and time consuming, requiring expensive equipment and highly skilled personnel. Therefore, these assays have not found acceptance except in few research centers.
2. Description of the Prior Art
Methods for measuring 1,25-dihydroxyvitamin D.sub.3 are described in Brumbaugh et al., Biochem. 1974; 13:4091-4097; Clemens et al., Clin. Sci. Mol. Med. 1978; 54:329-332; Schaefer and Goldsmith, in Normann, et al., Eds. Vitamin D Basic Research and Its Clinical Application, New York, Walter de Gruyter, 1979, pages 205-212.